Hi Doctor, I've Been Having A Problem For Around 4/5

Hi doctor, I've been having a problem for around 4/5 months where my penis has become very tight when I get an erection and try to have sex with my partner. A week ago I noticed that like the ( person on in the last comment) I have a thining of the skin at the end of my penis with like a rash . But in this case when I went to wash myself there was blood on the toilet paper. It had come from the rash and not from where the sperm comes out. Tonight we was going to have sex again and I found that it was very sore and I could not pull my foreskin back and as I tryed to put my penis in her , the pain was too much. Please can you help. Ps, I know this is not a STI 100% Thank you